Keeping in mind that not all solutions are simple or canned. Many organizations sell sophisticated, tailored solutions and may require multiple engagements and cultivation of a lead before determining what, if any opportunity there is. A robust lead stage, complete with linked activities, contacts, etc that can be converted to a deal (opportunity) is really valuable to any pipeline management. I know our view of our market (which I believe is pretty standard) is PROSPECT (all non-customers we're targeting with marketing to convert into leads), LEAD (marketing or out-bound qualified leads that sales is now working in order to quantify an opportunity), OPPORTUNITY (a lead that now has a quantified opportunity and value assigned (deal in your lexicon). Within the LEAD phase, for us, we may do discovery and demo before we convert to an OPPORTUNITY because we will tailor the solution based on those engagements. Make Leads tracking great again! :D 
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